On the banks of the Río Huana Mayu, in the upper Potosí barrios of Cantumarca and San Antonio, are some fine ruined examples of the ingenios (smelters) formerly used to extract silver from the ore hauled out of Cerro Rico. Some remaining ones – there were originally 82 along a 15km stretch – date back to the 1570s and were in use until the mid-1800s. Most Cerro Rico mine tours include a stop at a working ingenio.
Each ingenio consists of a floor penetrated by shallow wells (buitrones) where the ore was mixed with mercury and salt. The ore was then ground by millstones that were powered by water that was impounded in the 32 artificial Lagunas de Kari Kari.